JP7260660B2 - Solid electrolyte material, solid electrolyte, method for producing solid electrolyte, and all-solid battery - Google Patents

Description

One embodiment of the present invention relates to a solid electrolyte material, a solid electrolyte, a method for producing a solid electrolyte, or an all-solid battery.

In recent years, there has been a demand for the development of high-output and high-capacity batteries as power sources for notebook computers, tablet terminals, mobile phones, smart phones, electric vehicles (EVs), and the like. Among them, an all-solid battery using a solid electrolyte instead of a liquid electrolyte such as an organic solvent is attracting attention as a battery excellent in charge/discharge efficiency, charging speed, safety and productivity.

As the solid electrolyte, an inorganic solid electrolyte attracts attention, and as the inorganic solid electrolyte, mainly oxide-based and sulfide-based solid electrolytes are known.
Using a sulfide-based solid electrolyte has the advantage of being able to fabricate batteries by cold pressing, etc., but it is unstable against humidity and may generate harmful hydrogen sulfide gas, so it is safe. Development of oxide-based solid electrolytes is progressing from the viewpoint of properties and the like.

As such an oxide-based solid electrolyte, Non-Patent Document 1 discloses that LiTa ₂ PO ₈ having a monoclinic crystal structure exhibits high lithium ion conductivity (total conductivity (25° C.): 2.5× 10 ⁻⁴ S·cm ⁻¹ ).

J. Kim et al., J. Mater. Chem. A, 2018, 6, p22478-22482

Oxide-based solid electrolytes have extremely high grain boundary resistance, and in order to obtain sufficient ionic conductivity for use in all-solid-state batteries, solid electrolyte powders must not only be pressure-molded, but must also be made into a high-density sintered body. There is a need. In order to obtain such a high-density sintered body, it has been necessary to sinter at a high temperature of about 1100° C., for example.
Moreover, when producing an all-solid-state battery using an oxide-based solid electrolyte, it is necessary to sinter it together with a positive electrode material, a negative electrode material, etc. in order to obtain high ion conductivity.

At the time of these firings, in order to suppress the decomposition and deterioration of other materials such as positive electrode and negative electrode materials, in terms of economic efficiency and equipment, high ion Although it is desired to obtain a sintered body with sufficient conductivity, when the LiTa ₂ PO ₈ described in Non-Patent Document 1 is fired at a low temperature, it is impossible to obtain a sintered body exhibiting sufficient ionic conductivity. could not.

One embodiment of the present invention provides a solid electrolyte material capable of obtaining a sintered body with sufficient ionic conductivity even when fired at a low temperature (eg, 900° C. or lower).

As a result of intensive studies, the inventors of the present invention have found that the above problems can be solved by the following configuration example, and have completed the present invention.
A configuration example of the present invention is as follows.

[1] An amorphous solid electrolyte material containing lithium, tantalum, phosphorus and oxygen as constituent elements and having a phosphorus element content of more than 5.3 atomic % and less than 8.3 atomic %.

[2] The solid electrolyte material according to [1], which has a tantalum element content of 10.6 to 16.6 atomic percent.
[3] The solid electrolyte material according to [1] or [2], wherein the lithium element content is 5.0 to 20.0 atomic percent.
[4] containing one or more elements selected from the group consisting of B, Bi, Nb, Zr, Ga, Sn, Hf, W, Mo, Si, Al and Ge as constituent elements [1] to [3] Solid electrolyte material according to any one of.

[5] A solid electrolyte obtained using the solid electrolyte material according to any one of [1] to [4].

[6] A solid electrolyte, which is a sintered body of the solid electrolyte material according to any one of [1] to [4].
[7] A method for producing the solid electrolyte according to [5] or [6], comprising firing the solid electrolyte material according to any one of [1] to [4] at 500 to 900°C.

[8] a positive electrode having a positive electrode active material;
a negative electrode having a negative electrode active material;
a solid electrolyte layer between the positive electrode and the negative electrode;
including
The solid electrolyte layer contains the solid electrolyte according to [5] or [6],
All-solid battery.

[9] The cathode active material is _LiM3PO4 [M3 is one or more elements selected from the group consisting of Mn, Co, Ni, Fe, Al, Ti and V, or two elements of V and O; ], LiM5VO ₄ [M5 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al and Ti. ], Li ₂ M6P ₂ O ₇ [M6 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, Ti and V, or two elements of V and O. ], _LiVP2O7 , _Lix7Vy7M7z7 [ _2≤x7≤4 , 1≤y7≤3, 0≤z7≤1, 1≤y7+z7≤3, M7 is Ti _, Ge _, Al, Ga and Zr It is one or more elements selected from the group consisting of ], Li _1+x8 Al _x8 M8 _2-x8 (PO ₄ ) ₃ [0≦x8≦0.8, M8 is one or more elements selected from the group consisting of Ti and Ge. _] , LiNi1 _{/3Co1 / 3Mn1} / _3O2 , _LiCoO2 , _{LiNiO2 , LiMn2O4} , _{Li2CoP2O7 , Li3V2} ( _PO4 ) _{3 , Li3Fe2 ( PO4 ) 3 , LiNi0.5Mn1.5O4 and Li4Ti5O12 .}

[10] The negative electrode active material is _LiM3PO4 [M3 is one or more elements selected from the group consisting of Mn, Co, Ni, Fe, Al, Ti and V, or two elements of V and O; ], LiM5VO ₄ [M5 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al and Ti. ], Li ₂ M6P ₂ O ₇ [M6 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, Ti and V, or two elements of V and O. ], _LiVP2O7 , _Lix7Vy7M7z7 [ _2≤x7≤4 , 1≤y7≤3, 0≤z7≤1, 1≤y7+z7≤3, M7 is Ti _, Ge _, Al, Ga and Zr It is one or more elements selected from the group consisting of ], Li _1+x8 Al _x8 M8 _2-x8 (PO ₄ ) ₃ [0≦x8≦0.8, M8 is one or more elements selected from the group consisting of Ti and Ge. ], ( _{Li3-a9x9+(5-b9)y9M9x9 )} (V1 _{- y9M10y9} ) _O4 [M9 is one or more elements selected from the group consisting of Mg, Al, Ga and Zn; , M10 are one or more elements selected from the group consisting of Zn, Al, Ga, Si, Ge, P and Ti, 0≦x9≦1.0, 0≦y9≦0.6, a9 is M9 and b9 is the average valence of M10. ], LiNb ₂ O ₇ , Li ₄ Ti ₅ O ₁₂ , Li ₄ Ti ₅ PO ₁₂ , TiO ₂ , LiSi and graphite. All-solid-state battery.

[11] The all-solid battery according to any one of [8] to [10], wherein the positive electrode and the negative electrode contain the solid electrolyte according to [5] or [6].

According to one embodiment of the present invention, it is possible to obtain a sintered body with sufficient ion conductivity, particularly sufficient lithium ion conductivity, even when fired at a low temperature (eg, 900° C. or less). Therefore, by using the solid electrolyte material according to one embodiment of the present invention, it is possible to obtain a solid state material having sufficient ionic conductivity while being excellent in economic efficiency and suppressing decomposition and deterioration of other materials such as positive electrode and negative electrode materials. An all-solid-state battery containing an electrolyte can be easily produced.

1 is an XRD pattern of the solid electrolyte material obtained in Example 1. FIG. 4 is an XRD pattern of the solid electrolyte material obtained in Comparative Example 4. FIG.

≪Solid electrolyte material≫
A solid electrolyte material according to an embodiment of the present invention (hereinafter also referred to as "the present material") is amorphous, contains lithium, tantalum, phosphorus and oxygen as constituent elements, and has a phosphorus element content of It is more than 5.3 atomic % and less than 8.3 atomic %.

This material is amorphous. The present material is amorphous, for example, in the X-ray diffraction (XRD) pattern, no peak is observed (broad peak is observed), that is, observed in the range of 20 ° ≤ 2θ ≤ 40 °. It can be judged by the fact that the half width of the diffraction peak with the maximum intensity is larger than 0.15°. In other words, when the half width of the diffraction peak is 0.15° or less, it is judged to be crystalline.
Since the present material is amorphous, a solid electrolyte obtained from the present material, particularly a solid electrolyte (sintered body) obtained by firing the present material, tends to exhibit higher ionic conductivity.

The shape, size, etc. of the present material are not particularly limited, but it is preferably particulate (powder), and the average particle diameter (D50) of the present material is preferably 0.1 to 10 μm, more preferably 0.1 μm. 1 to 5 μm.
When the average particle size of the present material is within the above range, the solid electrolyte obtained from the present material, particularly the solid electrolyte (sintered body) obtained by firing the present material, tends to exhibit higher ionic conductivity. It is in.

Elements constituting this material are not particularly limited as long as they include lithium, tantalum, phosphorus and oxygen, and the group consisting of B, Bi, Nb, Zr, Ga, Sn, Hf, W, Mo, Si, Al and Ge. It may contain one or more selected elements.

The content of lithium element in the present material is preferably 5.0 to 20.0 atomic %, more preferably 9.0 atomic %, from the viewpoint that a solid electrolyte with higher lithium ion conductivity can be easily obtained. ~15.0 atomic percent.

The content of each element in this material is determined using a standard powder sample containing Mn, Co, and Ni in a ratio of 1:1:1 as a lithium-containing transition metal oxide such as LiCoO ₂ , for example. , the absolute intensity quantification method of Auger Electron Spectroscopy (AES). Alternatively, it can be obtained by a conventionally known quantitative analysis. For example, after thermal decomposition by adding acid to the sample, the volume of the thermal decomposition product can be adjusted and the content of each element in the material can be determined using a high frequency inductively coupled plasma (ICP) emission spectrometer.

The content of the tantalum element in the present material is preferably 10.6 to 16.6 atomic %, more preferably 11.0 atomic %, from the viewpoint that a solid electrolyte with higher lithium ion conductivity can be easily obtained. ~16.0 atomic percent.

The content of elemental phosphorus in this material is more than 5.3 atomic % and less than 8.3 atomic %, because the sintering temperature for obtaining a sintered body with sufficient ionic conductivity can be lowered. preferably 5.5 atomic % or more and less than 8.3 atomic %, more preferably 5.5 atomic % or more and 8.2 atomic % or less, still more preferably 5.7 atomic % or more and 8.2 atomic % atomic % or less.

When the present material contains one or more elements selected from the group consisting of B, Bi, Nb, Zr, Ga, Sn, Hf, W, Mo, Si, Al and Ge, B, Bi, Each content of one or more elements selected from the group consisting of Nb, Zr, Ga, Sn, Hf, W, Mo, Si, Al and Ge facilitates obtaining a solid electrolyte exhibiting higher ionic conductivity. It is preferably 0.1 to 5.0 atomic %, more preferably 0.1 to 3.0 atomic %, because it tends to be possible to

<Manufacturing method of this material>
The present material contains lithium, tantalum, phosphorus and oxygen as constituent elements, for example, in a method (I) including a pulverization step of pulverizing (pulverizing and mixing) a material to be pulverized containing lithium, tantalum, phosphorus and oxygen as constituent elements. It is preferably prepared as component (Z).

In the pulverization step, the present material obtained is pulverized so as to be amorphous by a mechanochemical reaction. In this case, it is preferable to pulverize the present material so that the average particle size of the present material falls within the above range.

Examples of the pulverizing step include a method of pulverizing using a roll rolling mill, a ball mill, a small diameter ball mill (bead mill), a medium stirring mill, an airflow pulverizer, a mortar, an automatic kneading mortar, a tank disintegrator, a jet mill, and the like. be done. Among these, when obtaining a solid electrolyte from the present material, a method of pulverizing using a ball mill or bead mill is preferable because a solid electrolyte exhibiting higher ionic conductivity can be easily obtained. A method of pulverizing with a ball mill using balls of 1 to 10 mm is more preferable.

The time for the pulverization step is preferably 0.5 to 48, because the material becomes amorphous due to the mechanochemical reaction and the average particle diameter (D50) is within the above range. hours, more preferably 2 to 48 hours.

In the pulverization step, the mixture may be mixed while pulverizing while heating if necessary, but it is usually carried out at room temperature.
The pulverization step may be performed in the atmosphere, but is preferably performed in an atmosphere of nitrogen gas and/or argon gas with an oxygen gas content adjusted in the range of 0 to 20% by volume.

The raw material used for the material to be pulverized is preferably an inorganic compound from the viewpoint of ease of handling.
The raw material may be obtained by manufacturing by a conventionally known method, or a commercially available product may be used.

As the method (I), for example,
Method (i) using a compound containing a lithium atom, a compound containing a tantalum atom, and a compound containing a phosphorus atom as the materials to be pulverized can be mentioned.

Examples of compounds containing lithium atoms include lithium carbonate (Li ₂ CO ₃ ), lithium oxide (Li ₂ O), lithium hydroxide (LiOH), lithium acetate (LiCH ₃ COO) and hydrates thereof. . Among these, lithium carbonate, lithium hydroxide, and lithium acetate are preferable because they are easily decomposed and reacted.
One type of compound containing a lithium atom may be used, or two or more types may be used.

Examples of compounds containing tantalum atoms include tantalum pentoxide (Ta ₂ O ₅ ) and tantalum nitrate (Ta(NO ₃ ) ₅ ). Among these, tantalum pentoxide is preferable from the viewpoint of cost.
One type of compound containing a tantalum atom may be used, or two or more types may be used.

As the compound containing a phosphorus atom, a phosphate is preferable. As the phosphate, since it is easily decomposed and reacted, for example, diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), dihydrogen phosphate _Ammonium ( _NH4H2PO4 ) may be _mentioned .
One type of compound containing a phosphorus atom may be used, or two or more types may be used.

When the present material contains one or more elements M1 selected from the group consisting of Bi, Nb, Zr, Ga, Sn, Hf, W and Mo, and/or the material is selected from the group consisting of B, Si, Al and Ge When the material to be pulverized contains a compound containing a lithium atom, a compound containing a tantalum atom, a compound containing a phosphorus atom, and/or a compound containing the element M1, and/or Alternatively, a method (i') using a compound containing the element M2 is exemplified.

Although the compound containing the element M1 is not particularly limited, it is preferably an inorganic compound from the viewpoint of ease of handling, and examples thereof include oxides and nitrates of M1. Among these, oxides are preferable from the viewpoint of cost.
One type of compound containing M1 may be used, or two or more types may be used.

When M1 is Nb, examples _of compounds containing _niobium atoms include _Nb2O5 , _LiNbO3 , _LiNb3O8 , and _NbPO5 .
One type of compound containing a niobium atom may be used, or two or more types may be used.

When M1 is Bi, examples of compounds _containing bismuth _atoms include _{LiBiO2 , Li3BiO3} , _Li4Bi2O5 , _{Li2.4Al0.2BiO3 , and Bi2O3 .}
One type of compound containing a bismuth atom may be used, or two or more types may be used.

When M1 is Ga or Sn, the oxides include gallium oxide (Ga ₂ O ₃ ), tin oxide (SnO ₂ ), and the like, respectively.

When M1 is Zr, Hf, W or Mo, the oxides include zirconium oxide (ZrO ₂ ), hafnium oxide (HfO ₂ ), tungsten oxide (WO ₃ ), molybdenum oxide (MoO ₃ ) and the like. be done. When M1 is Zr, Hf, W or Mo, in addition to the oxide, zirconium hydroxide (Zr(OH) 4 ), hafnium hydroxide (Hf(OH) ₄ ), hafnium hydroxide (Hf(OH) ₄ ), Tungstic _acid ( _H2WO4 ) and molybdic acid ( _H2MoO4 ) can also _be used.

Although the compound containing the element M2 is not particularly limited, it is preferably an inorganic compound from the viewpoint of ease of handling, and examples thereof include oxides of M2.
One type of compound containing the element M2 may be used, or two or more types may be used.

When M2 is B, examples of compounds containing boron atoms include LiBO ₂ , LiB ₃ O ₅ , Li ₂ B ₄ O ₇ , Li ₃ B ₁₁ O ₁₈ , Li ₃ BO ₃ , Li ₃ B ₇ O ₁₂ , _{Li4B2O5 , Li6B4O9 ,} Li3 _{-x5B1-x5Cx5O3 ( 0 <} x<1), _{Li4 -x6B2- x6Cx6O5 ( 0 < x6 <} 2 _{) , Li2.4Al0.2BO3} , _{Li2.7Al0.1BO3} , _{B2O3 , H3BO3 .}
One type of compound containing a boron atom may be used, or two or more types may be used.

When M2 is Si, _{the compound} containing _{a silicon} atom includes, for _example , _{SiO2 , Li2SiO3} , _{Li2Si2O5 , Li2Si3O7} , _{Li4SiO4 , Li6Si2O7} , Li ₈ SiO ₆ .
One type of compound containing a silicon atom may be used, or two or more types may be used.

When M2 is Ge or Al, the oxides include germanium oxide (GeO ₂ ), aluminum oxide (Al ₂ O ₃ ), and the like, respectively.

The mixing ratio of the raw materials may be, for example, such that the content of each constituent element in the present material to be obtained is within the above range.
Since lithium atoms tend to flow out of the system in the later-described firing step, the compound containing lithium atoms may be used in excess of about 10% to 20%.
In addition, in the firing step described later, the compound containing a phosphorus atom may be used in excess of about 0.1 to 10% in order to suppress the generation of by-products.

In method (i) and method (i′), each raw material may be mixed in advance before the pulverization step, but in the pulverization step, each raw material is pulverized and mixed (pulverized and mixed). is preferred.

Further, as the method (I), for example,
Method (ii) using a compound (a) containing lithium, tantalum, phosphorus and oxygen as constituent elements and a phosphorus compound (b) (hereinafter also simply referred to as compound (b)) as the material to be pulverized, or
As the material to be pulverized, a compound (c) containing lithium, tantalum, phosphorus and oxygen as constituent elements [wherein the compound (c) is a compound having a phosphorus element content within the above range. ] is also included.
In addition, methods (ii) and (iii) may further use a compound containing the element M1 and/or a compound containing the element M2.

In method (ii), compound (a) and compound (b) may be mixed in advance before the pulverization step. Mixing while pulverizing (pulverizing and mixing) is preferred.

・Compound (a)
The compound (a) is a compound containing lithium, tantalum, phosphorus and oxygen as constituent elements, preferably an oxide containing these elements, and preferably a lithium ion conductive compound containing these elements. more preferred.
The compound (a) may be the same compound as the compound (c), and the phosphorus element content of the compound (a) may be below the lower limit of the above range.
The compound (a) used in method (ii) may be one kind or two or more kinds.

Compound (a) is preferably a compound having a monoclinic structure. Whether compound (a) has a monoclinic structure is determined, for example, by Rietveld analysis of the X-ray diffraction (XRD) pattern of compound (a), specifically by the method of the following example. be able to.

Specifically, the compound (a) contains lithium, tantalum, phosphorus and oxygen as constituent elements, and at least one selected from the group consisting of Bi, Nb, Zr, Ga, Sn, Hf, W and Mo. The compound (a1) which may contain the element M1 of, contains lithium, tantalum, phosphorus and oxygen as constituent elements, and further contains one or more elements M2 selected from the group consisting of B, Si, Al and Ge compound (a2) which may be Among these, the compound (a) is preferably a compound containing only lithium, tantalum, phosphorus and oxygen as the constituent elements, and more preferably LiTa ₂ PO ₈ , from the viewpoint that the effects of the present invention are exhibited more effectively. .

The compound (a1) is preferably LiTa ₂ PO ₈ or a compound in which part of Ta in LiTa ₂ PO ₈ is substituted with the element M1, and preferably has a monoclinic structure.
Specifically, the compound (a1) has a composition formula of Li[ _1+(5-a)x ]Ta _2-x M1 _x PO ₈ [M1 is Bi, Nb, Zr, Ga, Sn, Hf, W and It is one or more elements selected from the group consisting of Mo, satisfies 0.0≦x<1.0, and a is the average valence of M1. ] It is preferable that it is a compound represented by.

In the solid electrolyte obtained using the compound (a), M1 is more preferably Bi, Nb, W, or Mo, and more preferably Bi, Nb, or W, because the lithium ion conductivity at the grain boundary is increased. Bi and Nb are particularly preferred.

The x is preferably 0.95 or less, more preferably 0.90 or less, still more preferably 0.85 or less, more preferably 0.80 or less, and particularly preferably 0.75 or less.
When x is within the above range, the solid electrolyte obtained using the compound (a) tends to have high lithium ion conductivity at grain boundaries.

Depending on the valence and content of M1, the amount of Li varies according to the average valence of M1 so that the aforementioned compound (a) can be neutral in charge. The average valence represented by a can be obtained as follows. When M1 is composed of two or more elements, the a is calculated by weighted average using the valence of each element and the content of each element. For example, when M1 is composed of 80 atomic % Nb and 20 atomic % Zr, a is calculated as (+5×0.8)+(+4×0.2)=+4.8. When M1 is composed of 80 atomic % Nb and 20 atomic % W, a is calculated as (+5×0.8)+(+6×0.2)=+5.2.

The compound (a2) is preferably LiTa ₂ PO ₈ or a compound in which part of P in LiTa ₂ PO ₈ is substituted with the element M2, and preferably has a monoclinic structure.
Specifically, the compound (a2) has a composition formula of Li[ _1+(5-b)y ]Ta ₂ P _1-y M2 _y O ₈ [M2 is selected from the group consisting of B, Si, Al and Ge. 0.0≦y<0.7, and b is the average valence of M2. ] It is preferable that it is a compound represented by.

In the solid electrolyte obtained using the compound (a), M2 is more preferably B, Si or Al, more preferably B or Si, in terms of increasing lithium ion conductivity at grain boundaries.

The y is preferably 0.65 or less, more preferably 0.60 or less, and still more preferably 0.55 or less.
When y is within the above range, the solid electrolyte obtained using the compound (a) tends to have a high total ion conductivity, which is the sum of the lithium ion conductivity in the crystal grains and at the crystal grain boundaries.

The average valence represented by b can be obtained in the same manner as the method for calculating the average valence a described above.

The method for producing compound (a) is not particularly limited, and conventionally known production methods such as solid-phase reaction and liquid-phase reaction can be employed. Specific examples of the manufacturing method include a method including at least one step of mixing step and one step of firing step.

The mixing step in the method for producing the compound (a) includes, for example, the raw materials, a compound containing a lithium atom (e.g. oxide, carbonate), a compound containing a tantalum atom (e.g. oxide, nitrate), A step of mixing a compound containing a phosphorus atom (e.g. ammonium salt) and, if necessary, a compound containing element M1 (e.g. oxide) and/or a compound containing element M2 (e.g. oxide). be done.
For each of the raw materials, one kind may be used, or two or more kinds may be used.

Examples of the method of mixing the raw materials include a method of mixing using a roll rolling mill, a ball mill, a small diameter ball mill (bead mill), a medium stirring mill, an air flow grinder, a mortar, an automatic kneading mortar, a tank disintegrator, a jet mill, and the like. is mentioned.

The raw materials may be mixed at a stoichiometric ratio, for example, so as to obtain the desired composition of compound (a).
Since lithium atoms tend to flow out of the system in the later-described firing step, the compound containing lithium atoms may be used in excess of about 10% to 20%. In addition, in the firing step described later, the compound containing a phosphorus atom may be used in excess of about 0.1 to 10% in order to suppress the generation of by-products.

Although the mixing may be performed while heating if necessary, the mixing is usually performed at room temperature.
The mixing may be performed in the atmosphere, but is preferably performed in an atmosphere of nitrogen gas and/or argon gas with an oxygen gas content adjusted in the range of 0 to 20% by volume.

In the firing step in the method for producing compound (a), the mixture obtained in the mixing step is fired. When the firing step is performed multiple times, a grinding step using a ball mill, mortar, or the like may be provided for the purpose of pulverizing or reducing the particle size of the fired product obtained in the firing step. In particular, since the compound (a) has a slow phase generation reaction rate, a reaction intermediate may be present in the first firing. In this case, it is preferable to carry out the firing process for the first time, perform the pulverization process, and then carry out the firing process.

The firing step may be performed in the atmosphere, but is preferably performed in an atmosphere of nitrogen gas and/or argon gas with an oxygen gas content adjusted in the range of 0 to 20% by volume.

The firing temperature is preferably 800 to 1200°C, more preferably 950 to 1100°C, still more preferably 950 to 1000°C, although it depends on the firing time.
When the firing temperature is within the above range, lithium atoms are less likely to flow out of the system, and a compound (a) with high ionic conductivity tends to be obtained.

The firing time (the total firing time when the firing process is performed several times) is preferably 1 to 16 hours, more preferably 3 to 12 hours, depending on the firing temperature.
When the firing time is within the above range, lithium atoms are less likely to flow out of the system, and a compound with high ionic conductivity tends to be obtained.

If the fired product obtained after the firing step is left in the air, it may absorb moisture or react with carbon dioxide to deteriorate. For this reason, it is preferable that the fired product obtained after the firing step is transferred to a dehumidified inert gas atmosphere and stored when the temperature reaches 200° C. or less in the temperature drop after the firing step.

- Phosphorus compound (b)
Phosphorus compound (b) is a compound different from compound (a).
The compound (b) used in method (ii) may be one kind or two or more kinds.

Compound (b) is preferably an inorganic compound from the viewpoint of ease of handling.
Compound (b) may be produced by a conventionally known method, or a commercially available product may be used.

Compound (b) is preferably a crystalline compound. Whether compound (b) is a crystalline compound can be determined, for example, from the X-ray diffraction (XRD) pattern of compound (b).

As the compound (b), for example, a phosphate is preferable, and since the phosphate is easily decomposed and reacted, for example, diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), dihydrogen phosphate monoammonium (NH ₄ H ₂ PO ₄ ).
Also, as the phosphorus compound, for example, LiPO ₃ and Li ₃ PO ₄ may be used.

In method (ii), it is preferable to use compound (a) and compound (b) in such an amount that the content of each constituent element in the present material to be obtained is within the above range.

・Compound (c)
Compound (c) is a compound containing lithium, tantalum, phosphorus and oxygen as constituent elements, preferably an oxide containing these elements, and preferably a lithium ion conductive compound containing these elements. more preferred.
However, the compound (c) is a compound having a phosphorus element content within the above range.

Compound (c) is preferably a compound having a monoclinic structure. Whether compound (c) has a monoclinic structure is determined, for example, by Rietveld analysis of the X-ray diffraction (XRD) pattern of compound (c), specifically by the method of the following example. be able to.

The method for producing compound (c) is not particularly limited, and examples thereof include the same production method as for compound (a).
For the same reason as in the production of compound (a), it is preferable to transfer and store in a dehumidified inert gas atmosphere as in the production of compound (a).

≪Solid electrolyte≫
A solid electrolyte according to an embodiment of the present invention (hereinafter also referred to as "the present electrolyte") is obtained using the present material, and is preferably a sintered body of the present material obtained by firing the present material. .

The electrolyte preferably has a monoclinic structure. Whether the solid electrolyte has a monoclinic structure can be determined, for example, by Rietveld analysis of the X-ray diffraction (XRD) pattern of the solid electrolyte, specifically by the method of the following examples.
The monoclinic crystal ratio (= monoclinic crystal content × 100/total crystal content of confirmed crystals) of the present electrolyte is preferably 70% or more, more preferably 80% or more, and still more preferably 90% or more. , the upper limit is 100%, although not particularly limited.
When the monoclinic crystal fraction of the present electrolyte is within the above range, the solid electrolyte tends to have high ionic conductivity both inside the crystal grains and at the crystal grain boundaries.

The total ion conductivity of the sintered body of the present material obtained by firing the present material at 850° C. or higher and 900° C. or lower is preferably 2.00×10 ⁻⁴ S·cm ⁻¹ or more, more preferably 3.00. ×10 ^-4 S·cm ^-1 or more.
The total ion conductivity of the sintered body of the present material obtained by firing the present material at 750° C. or more and less than 850° C. is preferably 4.00×10 ⁻⁵ S·cm ⁻¹ or more, more preferably 8.00. ×10 ^-5 S·cm ^-1 or more.
The total ion conductivity of the sintered body of the present material obtained by firing the present material at 700° C. or higher and lower than 750° C. is preferably 2.00×10 ⁻⁵ S·cm ⁻¹ or more, more preferably 4.00. ×10 ^-5 S·cm ^-1 or more.
The total ion conductivity of the sintered body of the present material obtained by firing the present material at 650° C. or higher and lower than 700° C. is preferably 1.00×10 ⁻⁵ S·cm ⁻¹ or more, more preferably 2.00. ×10 ^-5 S·cm ^-1 or more.
When the total ionic conductivity is within the above range, the sintered body obtained by firing the present material at a low temperature can be said to have sufficient ionic conductivity.
Specifically, the total ionic conductivity can be measured by the method described in Examples below.

<Method for producing the present electrolyte>
The method for producing the present electrolyte preferably includes a step A of firing the present material, and more preferably a method in which the present material is molded and then fired to form a sintered body.

The firing temperature in step A is preferably 500 to 900°C, more preferably 600 to 850°C, still more preferably 650 to 850°C.
Since this material is used, a sintered body with sufficient ionic conductivity can be obtained even if it is fired at such a low temperature.

The firing time in step A is preferably 12 to 144 hours, more preferably 48 to 96 hours, depending on the firing temperature.
When the firing time is within the above range, a sintered body with sufficient ionic conductivity can be obtained even when fired at a low temperature.

The firing in step A may be performed in the air, but is preferably performed in an atmosphere of nitrogen gas and/or argon gas with an oxygen gas content adjusted in the range of 0 to 20% by volume.
Moreover, the firing in the step A may be performed in a reducing gas atmosphere such as a nitrogen-hydrogen mixed gas containing a reducing gas such as hydrogen gas. The ratio of hydrogen gas contained in the nitrogen-hydrogen mixed gas is, for example, 1 to 10% by volume. As the reducing gas, ammonia gas, carbon monoxide gas, etc. may be used in addition to hydrogen gas.

In the step A, it is preferable to sinter a molded body obtained by molding the present material, because a solid electrolyte (sintered body) having a higher ionic conductivity can be easily obtained, and the material is press-molded. It is more preferable to bake the compact.
The pressure for press molding this material is not particularly limited, but is preferably 50 to 500 MPa, more preferably 100 to 400 MPa.
The shape of the compact obtained by press-molding the present material is also not particularly limited, but the shape is preferably in accordance with the application of the sintered body (solid electrolyte) obtained by sintering the compact.

In addition, when producing the present electrolyte, components other than the present material may be used. Examples of the other components include conventionally known materials used in solid electrolytes of all-solid-state batteries. For example, lithium ion conductive compounds include lithium ion conductive materials having structures such as NASICON type and LISICON type. be done.
Each of the other components may be used alone or in combination of two or more.
The amount of the other components used is preferably 50% by mass or less, more preferably 30% by mass or less with respect to 100% by mass in total with the present material, and it is preferable not to use the other components.

≪All solid state battery≫
An all-solid-state battery according to one embodiment of the present invention (hereinafter also referred to as "this battery") includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a solid electrolyte between the positive electrode and the negative electrode layer, wherein the solid electrolyte layer contains the present electrolyte.
The battery of the present invention may be a primary battery or a secondary battery, but is preferably a secondary battery from the viewpoint of exhibiting the effects of the present invention more, and a lithium ion secondary battery. is more preferable.
The structure of the present battery is not particularly limited as long as it includes a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode.

<Solid electrolyte layer>
The solid electrolyte layer is not particularly limited as long as it contains the present electrolyte, and if necessary, may contain conventionally known additives used in solid electrolyte layers of all-solid-state batteries, but is preferably composed of the present electrolyte.
The thickness of the solid electrolyte layer may be appropriately selected according to the structure of the battery to be formed (thin film type, etc.), preferably 50 nm to 1000 μm, more preferably 100 nm to 100 μm.

<Positive electrode>
The positive electrode is not particularly limited as long as it has a positive electrode active material, but preferably includes a positive electrode having a positive electrode current collector and a positive electrode active material layer.

[Positive electrode active material layer]
The positive electrode active material layer is not particularly limited as long as it contains a positive electrode active material, but preferably contains a positive electrode active material and a solid electrolyte, and may further contain additives such as a conductive aid and a sintering aid. .
The thickness of the positive electrode active material layer may be appropriately selected according to the structure of the battery to be formed (thin film type, etc.), preferably 10 to 200 μm, more preferably 30 to 150 μm, further preferably 50 to 100 μm. .

Positive electrode active material Examples of positive electrode active materials include LiCo oxide, LiNiCo oxide, LiNiCoMn oxide, LiNiMn oxide, LiMn oxide, LiMn spinel, LiMnNi oxide, LiMnAl oxide, LiMnMg oxide, and LiMnCo oxide. LiMnFe oxide, LiMnZn oxide, LiCrNiMn oxide, LiCrMn oxide, lithium titanate, lithium metal phosphate, transition metal oxide, titanium sulfide, graphite, hard carbon, transition metal-containing lithium nitride, silicon oxide, Lithium silicate, lithium metal, lithium alloys, Li-containing solid solutions, and lithium-storage intermetallic compounds.
Among these, it has a good affinity with solid electrolytes, an excellent balance of macro-, micro-, and ionic conductivity, a high average potential, and a balance between specific capacity and stability. LiNiCoMn oxide, LiNiCo oxide, and LiCo oxide are preferable, and LiNiCoMn oxide is more preferable, from the viewpoint that the capacity can be increased.
Moreover, the surface of the positive electrode active material may be coated with an ion-conductive oxide such as lithium niobate, lithium phosphate, or lithium borate.
The positive electrode active material used in the positive electrode active material layer may be of one type or two or more types.

Preferred examples of the positive electrode active material include _LiM3PO4 [M3 is one or more elements selected from the group consisting of Mn, Co, Ni, Fe, Al, Ti and V, or two elements of V and O. . ], LiM5VO ₄ [M5 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al and Ti. ], Li ₂ M6P ₂ O ₇ [M6 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, Ti and V, or two elements of V and O. ], _LiVP2O7 , _Lix7Vy7M7z7 [ _2≤x7≤4 , 1≤y7≤3, 0≤z7≤1, 1≤y7 ₊ z7≤3, M7 is Ti _, Ge, Al, Ga and Zr It is one or more elements selected from the group consisting of ], Li _1+x8 Al _x8 M8 _2-x8 (PO ₄ ) ₃ [0≦x8≦0.8, M8 is one or more elements selected from the group consisting of Ti and Ge. _] , LiNi1 _{/3Co1 / 3Mn1} / _3O2 , _LiCoO2 , _{LiNiO2 , LiMn2O4} , _{Li2CoP2O7 , Li3V2} ( _PO4 ) _{3 , Li3Fe2 ( PO4 ) 3 , LiNi0.5Mn1.5O4, Li4Ti5O12 may also be mentioned} .

The positive electrode active material is preferably particulate. The 50% diameter in the volume-based particle size distribution is preferably 0.1-30 μm, more preferably 0.3-20 μm, still more preferably 0.4-10 μm, and particularly preferably 0.5-3 μm.
In addition, the ratio of the length of the major axis to the length of the minor axis (length of the major axis/length of the minor axis), that is, the aspect ratio of the positive electrode active material is preferably less than 3, more preferably less than 2.

The positive electrode active material may form secondary particles. In that case, the 50% diameter in the number-based particle size distribution of the primary particles is preferably 0.1 to 20 μm, more preferably 0.3 to 15 μm, even more preferably 0.4 to 10 μm, particularly preferably 0.5 to 2 μm. is.

The content of the positive electrode active material in the positive electrode active material layer is preferably 20 to 80% by volume, more preferably 30 to 70% by volume.
When the content of the positive electrode active material is within the above range, the positive electrode active material functions favorably, and there is a tendency to easily obtain a battery with a high energy density.

- Solid electrolyte The solid electrolyte that can be used in the positive electrode active material layer is not particularly limited, and conventionally known solid electrolytes can be used. is preferred.
One type or two or more types of solid electrolytes may be used in the positive electrode active material layer.

Additive Preferable examples of the conductive aid include metal materials such as Ag, Au, Pd, Pt, Cu, and Sn, and carbon materials such as acetylene black, ketjen black, carbon nanotubes, and carbon nanofibers.
As the sintering aid, the compound (b), a compound containing a boron atom, a compound containing a niobium atom, a compound containing a bismuth atom, and a compound containing a silicon atom are preferable.
Each of the additives used in the positive electrode active material layer may be one kind, or two or more kinds.

- Positive electrode current collector The positive electrode current collector is not particularly limited as long as the material conducts electrons without causing an electrochemical reaction. Materials for the positive electrode current collector include, for example, simple metals such as copper, aluminum, and iron, alloys containing these metals, and conductive metal oxides such as antimony-doped tin oxide (ATO) and tin-doped indium oxide (ITO). is mentioned.
As the positive electrode current collector, a current collector having a conductive adhesive layer provided on the surface of a conductor can also be used. Examples of the conductive adhesive layer include a layer containing a granular conductive material, a fibrous conductive material, or the like.

<Negative Electrode>
The negative electrode is not particularly limited as long as it has a negative electrode active material, but preferably includes a negative electrode having a negative electrode current collector and a negative electrode active material layer.

[Negative electrode active material layer]
The negative electrode active material layer is not particularly limited as long as it contains the negative electrode active material, but preferably contains the negative electrode active material and the solid electrolyte, and may further contain additives such as a conductive aid and a sintering aid. .
The thickness of the negative electrode active material layer may be appropriately selected according to the structure of the battery to be formed (thin film type, etc.), but is preferably 10 to 200 μm, more preferably 30 to 150 μm, and still more preferably 50 to 100 μm. .

Negative electrode active material Examples of negative electrode active materials include lithium alloys, metal oxides, graphite, hard carbon, soft carbon, silicon, silicon alloys, silicon oxide SiO _n (0<n≦2), and silicon/carbon composite materials. , composite materials containing silicon domains in the pores of porous carbon, lithium titanate, and graphite coated with lithium titanate.
Among these, a silicon/carbon composite material and a composite material in which silicon domains are included in the pores of porous carbon are preferable because they have a high specific capacity and can increase energy density and battery capacity. More preferably, it is a composite material in which silicon domains are included in the pores of porous carbon, which is excellent in mitigation of volume expansion accompanying lithium absorption/desorption of silicon, and has macro-, micro-, and ionic conductivity. Able to maintain good balance. Particularly preferably, the silicon domain is amorphous, the size of the silicon domain is 10 nm or less, and the porous carbon-derived pores are present in the vicinity of the silicon domain. It is an encapsulating composite material.

Preferred examples of the negative electrode active material include _LiM3PO4 [M3 is one or more elements selected from the group consisting of Mn, Co, Ni, Fe, Al, Ti and V, or two elements of V and O . ], LiM5VO ₄ [M5 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al and Ti. ], Li ₂ M6P ₂ O ₇ [M6 is one or more elements selected from the group consisting of Fe, Mn, Co, Ni, Al, Ti and V, or two elements of V and O. ], _LiVP2O7 , _Lix7Vy7M7z7 [ _2≤x7≤4 , 1≤y7≤3, 0≤z7≤1, 1≤y7 ₊ z7≤3, M7 is Ti _, Ge, Al, Ga and Zr It is one or more elements selected from the group consisting of ], Li _1+x8 Al _x8 M8 _2-x8 (PO ₄ ) ₃ [0≦x8≦0.8, M8 is one or more elements selected from the group consisting of Ti and Ge. ], ( _{Li3-a9x9+(5-b9)y9M9x9 )} (V1 _{- y9M10y9} ) _O4 [M9 is one or more elements selected from the group consisting of Mg, Al, Ga and Zn; , M10 are one or more elements selected from the group consisting of Zn, Al, Ga, Si, Ge, P and Ti, 0≦x9≦1.0, 0≦y9≦0.6, a9 is M9 and b9 is the average valence of M10. ], LiNb ₂ O ₇ , Li ₄ Ti ₅ O ₁₂ , Li ₄ Ti ₅ PO ₁₂ , TiO ₂ , LiSi and graphite.

The negative electrode active material is preferably particulate. The 50% diameter in the volume-based particle size distribution, the aspect ratio, and the 50% diameter in the number-based particle size distribution of the primary particles when the negative electrode active material forms secondary particles are in the same range as the positive electrode active material. Preferably.

The content of the negative electrode active material in the negative electrode active material layer is preferably 20 to 80% by volume, more preferably 30 to 70% by volume.
When the content of the negative electrode active material is within the above range, the negative electrode active material functions favorably, and there is a tendency to easily obtain a battery with a high energy density.

- Solid electrolyte The solid electrolyte that can be used in the negative electrode active material layer is not particularly limited, and conventionally known solid electrolytes can be used. is preferred.
One type or two or more types of solid electrolytes may be used in the negative electrode active material layer.

Additive Preferable examples of the conductive aid include metal materials such as Ag, Au, Pd, Pt, Cu, and Sn, and carbon materials such as acetylene black, ketjen black, carbon nanotubes, and carbon nanofibers.
As the sintering aid, the compound (b), a compound containing a boron atom, a compound containing a niobium atom, a compound containing a bismuth atom, and a compound containing a silicon atom are preferable.
One kind or two or more kinds of additives may be used for each of the negative electrode active material layers.

- Negative electrode current collector As the negative electrode current collector, the same current collector as the positive electrode current collector can be used.

<Method for manufacturing all-solid-state battery>
An all-solid-state battery can be formed, for example, by a known powder molding method. For example, the positive electrode current collector, the powder for the positive electrode active material layer, the powder for the solid electrolyte layer, the powder for the negative electrode active material layer, and the negative electrode current collector are superimposed in this order, and powder-molded at the same time. Formation of each layer of the positive electrode active material layer, the solid electrolyte layer and the negative electrode active material layer, and connection between the positive electrode current collector, the positive electrode active material layer, the solid electrolyte layer, the negative electrode active material layer and the negative electrode current collector can be done simultaneously.

During this powder compaction, it is preferable to sinter at the same temperature as the sintering temperature in the step A while applying a pressure similar to that in press molding the material in the step A.
According to one embodiment of the present invention, an all-solid-state battery exhibiting sufficient ion conductivity can be obtained even if the firing temperature for producing this all-solid-state battery is low. While suppressing the decomposition and deterioration of the material, it is economical and can produce an all-solid-state battery with less equipment.

Each layer of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer may be powder-molded. Baking is preferred.

Moreover, an all-solid-state battery can also be produced, for example, by the following method.
A paste for forming each layer is prepared by appropriately mixing a solvent, a resin, etc. with the material for forming the positive electrode active material layer, the material for forming the solid electrolyte layer, and the material for forming the negative electrode active material layer, and the paste is used as a base. A green sheet for a positive electrode active material layer, a green sheet for a solid electrolyte layer, and a green sheet for a negative electrode active material layer are produced by coating the sheets and drying them. Next, the green sheet for the positive electrode active material layer, the green sheet for the solid electrolyte layer, and the green sheet for the negative electrode active material layer, which are obtained by peeling off the base sheet from each green sheet, are successively laminated, thermocompression bonded at a predetermined pressure, and placed in a container. A laminate structure is fabricated by enclosing and pressing by hot isostatic pressing, cold isostatic pressing, isostatic pressing, or the like.

After that, if necessary, the laminated structure is degreased at a predetermined temperature and then fired to produce a laminated sintered body.
The firing temperature in this firing treatment is preferably the same as the firing temperature in step A above.

Next, if necessary, a positive electrode current collector and a negative electrode current collector are formed on both main surfaces of the laminated sintered body by a sputtering method, a vacuum deposition method, applying or dipping a metal paste, or the like, thereby forming an all-solid battery. It can also be produced.

EXAMPLES The present invention will be specifically described below based on examples. However, the present invention is not limited to these examples.

[Synthesis Example 1] Synthesis of Li ₃ BO ₃ Lithium hydroxide monohydrate (LiOH.H ₂ O) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 98.0% or more), and boric acid (H ₃ BO ₃ ) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.5% or higher) was weighed so that the atomic ratio (Li:B) of lithium and boron was 3.00:1.00. bottom. The weighed raw material powders were pulverized and mixed in an agate mortar for 15 minutes to obtain a mixture.

The resulting mixture is placed in an alumina boat and heated to 500°C at a heating rate of 10°C/min in an air atmosphere (flow rate: 100 mL/min) using a rotary kiln (manufactured by Motoyama Co., Ltd.). Then, it was sintered at 500° C. for 2 hours to obtain a primary sintered product.

The resulting primary fired product was pulverized and mixed in an agate mortar for 15 minutes, and the resulting mixture was placed in an alumina boat, using a rotary firing furnace (manufactured by Motoyama Co., Ltd.), in an air (flow rate: 100 mL / min) atmosphere. Then, the temperature was raised to 630° C. under the conditions of a temperature increase rate of 10° C./min, and firing was performed at 630° C. for 24 hours to obtain a secondary fired product (Li ₃ BO ₃ ).
After the obtained secondary calcined product was cooled to room temperature, it was taken out from the rotary calcining furnace, transferred to a dehumidified nitrogen gas atmosphere, and stored.

[Synthesis Example 2] Synthesis of Li ₄ B ₂ O ₅ Lithium hydroxide monohydrate (LiOH.H ₂ O) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 98.0% or more) and boric acid (H ₃ BO ₃ ) (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., purity 99.5% or higher) was added so that the atomic ratio (Li:B) of lithium and boron was 2.00:1.00. A secondary fired product (Li ₄ B ₂ O ₅ ) was obtained in the same manner as in Synthesis Example 1, except that it was weighed in .

[Synthesis Example 3] Synthesis of LiBiO ₂ Lithium hydroxide monohydrate (LiOH H ₂ O) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 98.0% or more) and bismuth oxide (Fujifilm Wako Kojunyaku Co., Ltd., purity 99.9%) was weighed so that the atomic ratio (Li:Bi) of lithium and bismuth was 1:1. The weighed raw material powders were pulverized and mixed in an agate mortar for 15 minutes to obtain a mixture.

The resulting mixture is placed in an alumina boat and heated to 600°C at a heating rate of 10°C/min in an air atmosphere (flow rate: 100 mL/min) using a rotary kiln (manufactured by Motoyama Co., Ltd.). Then, sintering was performed at 600° C. for 4 hours to obtain a sintered product (LiBiO ₂ ).
After cooling the obtained calcined product to room temperature, it was taken out from the rotary calcining furnace, transferred to a dehumidified nitrogen gas atmosphere, and stored.

[Example 1]
An appropriate amount of toluene was added to tantalum pentoxide (Ta ₂ O ₅ ) (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., purity 99.9%) and ground for 2 hours using a zirconia ball mill (zirconia balls: diameter 3 mm). .
Next, lithium carbonate (Li ₂ CO ₃ ) (manufactured by Sigma-Aldrich, purity 99.0% or more), the pulverized tantalum pentoxide (Ta ₂ O ₅ ), Li ₃ BO ₃ obtained in Synthesis Example 1 described above, and diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) (manufactured by Sigma-Aldrich, purity of 98% or higher) with an atomic ratio of lithium, tantalum, boron and phosphorus (Li:Ta:B:P) , Weighed so as to be as shown in Table 1, and furthermore, in order to suppress the formation of by-products in the baking process, diammonium hydrogen phosphate was added so that the amount of phosphorus atoms in Table 1 was multiplied by 1.065. weighed. An appropriate amount of toluene was added to each weighed raw material powder, and the mixture was pulverized and mixed for 2 hours using a zirconia ball mill (zirconia balls: diameter 1 mm) to prepare a solid electrolyte material.
The obtained solid electrolyte material was amorphous when evaluated by powder X-ray diffraction, which will be described later.

[Example 2]
An amorphous solid electrolyte material was produced in the same manner as in Example 1 except that the mixing ratio of the raw materials was changed so that the atomic ratio of lithium, tantalum, boron and phosphorus was the amount shown in Table 1. got

[Example 3]
In Example 1, silicon oxide (SiO ₂ ) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.9%) was further used, and the atomic ratio of lithium, tantalum, boron, phosphorus and silicon (Li:Ta: An amorphous solid electrolyte material was obtained in the same manner as in Example 1, except that the mixing ratio of the raw materials was changed so that B:P:Si) was the amount shown in Table 1.

[Examples 4-6]
Li ₄ B ₂ O ₅ obtained in Synthesis Example 2 was used in place of Li ₃ BO ₃ , and the raw material powders were prepared so that the atomic ratios of lithium, tantalum, boron and phosphorus were as shown in Table 1. An amorphous solid electrolyte material was obtained in the same manner as in Example 1, except that it was used.

[Example 7]
An appropriate amount of toluene was added to niobium pentoxide (Nb ₂ O ₅ ) (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., purity 99.9%) and ground for 2 hours using a zirconia ball mill (zirconia balls: diameter 3 mm). .
In Example 4, the pulverized niobium pentoxide (Nb ₂ O ₅ ) was further used, and raw material powders were used so that the atomic ratios of lithium, tantalum, niobium, boron and phosphorus were as shown in Table 1. An amorphous solid electrolyte material was obtained in the same manner as in Example 4, except for the above.

[Example 8]
In Example 4, instead of Li ₄ B ₂ O ₅ , boric acid (H ₃ BO ₃ ) (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., purity 99.5% or higher) was used, and lithium, tantalum, boron and An amorphous solid electrolyte material was obtained in the same manner as in Example 4, except that each raw material powder was used so that the atomic ratio of phosphorus was as shown in Table 1.

[Example 9]
In Example 1, instead of Li ₃ BO ₃ , silicon oxide (SiO ₂ ) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.9%) was used, and the atomic ratio of lithium, tantalum, phosphorus and silicon was An amorphous solid electrolyte material was obtained in the same manner as in Example 1, except that each raw material powder was used so that (Li:Ta:P:Si) was as shown in Table 1.

[Example 10]
LiBiO ₂ obtained in Synthesis Example 3 was used in place of Li ₃ BO ₃ in Example 1, and the atomic ratio (Li:Ta:Bi:P) of lithium, tantalum, bismuth and phosphorus was as shown in Table 1. An amorphous solid electrolyte material was obtained in the same manner as in Example 1, except that each raw material powder was used so that

[Comparative Example 1]
Lithium carbonate (Li ₂ CO ₃ ) (manufactured by Sigma-Aldrich, purity 99.0% or more), tantalum pentoxide (Ta ₂ O ₅ ) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.9%), and , diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) (manufactured by Sigma-Aldrich, purity 98% or more), and the atomic ratio (Li: Ta: P) of lithium, tantalum and phosphorus is as shown in Table 1. Considering the lithium atoms that flow out of the system in the firing process, weigh lithium carbonate so that the amount of lithium carbonate in Table 1 is 1.1 times the amount of lithium atoms, and further in the firing process, the auxiliary In order to suppress the formation of the product, diammonium hydrogen phosphate was weighed so that the phosphorus atomic weight in Table 1 was multiplied by 1.065. An appropriate amount of toluene was added to the weighed raw material powders, and pulverized and mixed for 2 hours using a zirconia ball mill (zirconia balls: diameter 1 mm).

The resulting mixture is placed in an alumina boat and heated to 1000°C at a heating rate of 10°C/min in an air atmosphere (flow rate: 100 mL/min) using a rotary kiln (manufactured by Motoyama Co., Ltd.). Then, it was sintered at 1000° C. for 4 hours to obtain a primary sintered product.

The resulting primary fired product was pulverized and mixed in an agate mortar for 15 minutes, and the resulting mixture was placed in an alumina boat, using a rotary firing furnace (manufactured by Motoyama Co., Ltd.), in an air (flow rate: 100 mL / min) atmosphere. Then, the temperature was raised to 1000° C. at a temperature increase rate of 10° C./min, and sintering was performed at 1000° C. for 1 hour to obtain a secondary sintered product.

An appropriate amount of toluene was added to the obtained baked product, and the mixture was pulverized and mixed for 2 hours using a zirconia ball mill (zirconia balls: diameter 1 mm) to obtain an amorphous solid electrolyte material.

[Comparative Example 2]
An amorphous solid electrolyte material was obtained in the same manner as in Comparative Example 1 except that the mixing ratio of the raw materials was changed so that the atomic ratio of lithium, tantalum and phosphorus was as shown in Table 1. rice field.

[Comparative Example 3]
In Example 3, except that the mixing ratio of the raw materials was changed so that the atomic number ratio of lithium, tantalum, boron, silicon and phosphorus was the amount shown in Table 1, it was produced in the same manner as in Example 3, An amorphous solid electrolyte material was obtained.

[Comparative Example 4]
Lithium carbonate (Li ₂ CO ₃ ) (manufactured by Sigma-Aldrich, purity 99.0% or more), tantalum pentoxide (Ta ₂ O ₅ ) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.9%), the above Li ₄ B ₂ O ₅ obtained in Synthesis Example 2 and diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) (manufactured by Sigma-Aldrich, purity 98% or higher) were combined with lithium, tantalum, boron and phosphorus. is weighed so that the atomic ratio is as shown in Table 1, and considering the lithium atoms that flow out of the system in the firing process, the amount of lithium carbonate is 1.1 times the lithium atomic weight in Table 1. Furthermore, in order to suppress the formation of by-products in the baking process, diammonium hydrogen phosphate was weighed so that the amount of phosphorus atoms in Table 1 was multiplied by 1.065. An appropriate amount of toluene was added to the weighed raw material powders, and pulverized and mixed for 2 hours using a zirconia ball mill (zirconia balls: diameter 1 mm).

The resulting mixture is placed in an alumina boat and heated to 1000°C at a heating rate of 10°C/min in an air atmosphere (flow rate: 100 mL/min) using a rotary kiln (manufactured by Motoyama Co., Ltd.). and sintered at 1000° C. for 4 hours to obtain a solid electrolyte material.
The resulting solid electrolyte material was evaluated by powder X-ray diffraction, which will be described later. As a result, the half width of the diffraction peak having the maximum intensity that can be confirmed in the range of 20° ≤ 2θ ≤ 40° was 0.12°. there were.

<Powder X-ray diffraction (XRD)>
Using a powder X-ray diffractometer PANalytical MPD (manufactured by Spectris Co., Ltd.), X-ray diffraction measurement of the obtained solid electrolyte material (Cu-Kα ray (output: 45 kV, 40 mA), diffraction angle 2θ = 10 to 50 ° range, step width: 0.013 °, incident side Sollerslit: 0.04 rad, incident side Anti-scatter slit: 2 °, light receiving side Sollerslit: 0.04 rad, light receiving side Anti-scatter slit: 5 mm), X-ray diffraction (XRD) patterns were obtained. The obtained XRD pattern is extracted from the well-known analysis software RIETAN-FP (created by Fujio Izumi's website "RIETAN-FP/VENUS system distribution file" (http://fujioizumi.verse.jp/download/download.html). The crystal structure was confirmed by performing Rietveld analysis using

XRD patterns of the solid electrolyte materials obtained in Example 1 and Comparative Example 4 are shown in FIGS. 1 and 2, respectively.
In Table 1, as in FIG. 1, the case where no peak can be confirmed (or the peak is broad) and is amorphous is defined as “amorphous”, and as shown in FIG. A case where the half-value width of the diffraction peak having the maximum intensity that can be confirmed in the range was 0.15° or less was defined as “crystalline”.

<Preparation of pellet>
A pressure of 40 MPa is applied to the obtained solid electrolyte material by a hydraulic press using a tableting machine to form a disk-shaped compact having a diameter of 10 mm and a thickness of 1 mm, followed by CIP (cold isostatic pressing). ), pellets were produced by applying a pressure of 300 MPa to the disk-shaped compact.

<Production of sintered body>
Put the obtained pellets in an alumina boat, use a rotary kiln (manufactured by Motoyama Co., Ltd.), in an atmosphere of air (flow rate: 100 mL / min), under the conditions of a temperature increase rate of 10 ° C. / min. The temperature was raised to the temperature (650° C., 700° C., 750° C. or 850° C.) indicated in the column of conductivity, and firing was performed at that temperature for 96 hours to obtain a sintered body.
After cooling the obtained sintered body to room temperature, it was taken out from the rotary sintering furnace, transferred to a dehumidified nitrogen gas atmosphere, and stored.

<Total conductivity>
A gold layer was formed on both surfaces of the obtained sintered body using a sputtering machine to obtain a measurement pellet for ionic conductivity evaluation.
The obtained measurement pellets were kept in a constant temperature bath at 25° C. for 2 hours before measurement. Then, at 25° C., using an impedance analyzer (manufactured by Solartron Analytical, model number: 1260A), AC impedance was measured in a frequency range of 1 Hz to 10 MHz under conditions of an amplitude of 25 mV. The obtained impedance spectrum is fitted with an equivalent circuit using the equivalent circuit analysis software ZView attached to the device to obtain the lithium ion conductivity in the crystal grain and the crystal grain boundary. degree was calculated. Table 1 shows the results. The total conductivity of the sintered body obtained by firing at 650° C. using the solid electrolyte material obtained in Comparative Example 1 was too low to obtain a measured value.

From Table 1, the amorphous solid electrolyte material containing lithium, tantalum, phosphorus and oxygen as constituent elements and having a phosphorus element content of more than 5.3 atomic % and less than 8.3 atomic % is 900 It can be seen that a sintered body with sufficient total conductivity can be obtained even when fired at a low temperature of 10°C or less.

Claims (4)

The constituent elements consist of lithium, tantalum, phosphorus and oxygen, and one or more elements selected from the group consisting of B, Bi, Nb and Si,
The phosphorus element content is 5.7 to 8.2 atomic %,
The tantalum element content is 12.9 to 16.4 atomic percent,
The lithium element content is 6.7 to 15.2 atomic percent,
When the boron element is included, the content of the boron element is 0.2 to 2.9 atomic %,
When the bismuth element is included, the content of the bismuth element is 0.4 atomic %,
When the niobium element is included, the content of the niobium element is 1.4 atomic %,
When silicon element is included, the content of silicon element is 1.4 to 1.6 atomic %.
A solid electrolyte material that is amorphous. A solid electrolyte obtained using the solid electrolyte material according to claim 1 . A solid electrolyte, which is a sintered body of the solid electrolyte material according to claim 1 . A method for producing a solid electrolyte according to claim 2 or 3, comprising a step of firing the solid electrolyte material according to claim 1 at 500 to 900°C.

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